1. Field of the Invention
The present invention relates to a dielectric ceramic composition, electronic device, and multilayer ceramic capacitor, more specifically relates to a dielectric ceramic composition making the ratio of the dielectric particles having a surface diffusion structure comprised of a main ingredient phase and a diffusion phase and of the dielectric particles having a domain in the main ingredient phase among dielectric particles forming the dielectric ceramic composition a certain range so as to realize a high temperature accelerated life, capacity-temperature characteristic, and dielectric constant which are all excellent.
2. Description of the Related Art
In recent years, electronic apparatuses have been rapidly made smaller in size and higher in performance. The electronic devices mounted in these electronic apparatuses are therefore also being required to be made smaller in size and higher in performance. As the characteristics required from multilayer ceramic capacitors, one example of an electronic device, a high dielectric constant, a long insulation resistance (IR) life, a good DC bias characteristic, and also a good temperature characteristic etc. may be mentioned.
Further, multilayer ceramic capacitors are being used not only in general electronic apparatuses, but also in engine electronic control units (ECU), crank angle sensors, antilock braking system (ABS) modules, or other various types of electronic apparatuses mounted in automobile engine compartments.
The environment in which, these electronic apparatuses are used falls in the winter in cold regions to as low as −20° C. or less. Further, after engine startup, in the summer, the temperature can be expected to rise to +130° C. or more. Recently, further, the wire harnesses connecting such electronic apparatuses and the equipment they control have been slashed and the electronic apparatuses have even been set outside the vehicles, so the environment of these electronic apparatuses has become even harsher. Therefore, the capacitors used in these electronic apparatuses are required to have flat temperature characteristics in a broad temperature range. Specifically, a dielectric ceramic composition must satisfy not only the X7R characteristic of the EIA standard (−55 to 125° C., ΔC/C=±15% or less), but also the X8R characteristic of the EIA standard (−55 to 150° C., ΔC/C=±15% or less).
As dielectric ceramic compositions satisfying the X8R characteristic, various proposals have been made. For example, Japanese Patent Publication (A) No. 2004-214539 discloses to calculate the average value of the concentration of Ca in the crystal particles and make its range of dispersion 5% or more in terms of CV value so as to obtain a capacitor satisfying the X8R characteristic and exhibiting an excellent CR product and high temperature accelerated life.
On the other hand, to realize a good dielectric constant and a good temperature characteristic, it is considered effective to make the dielectric particles forming a dielectric ceramic composition having BaTiO3 as a main ingredient a core-shell structure.
For example, Japanese Patent Publication (A) 2002-80276 discloses a dielectric ceramic composition characterized in that ceramic particles having a core-shell structure account for 15% or more of all ceramic particles and that the core parts have domains. However, a capacitor having dielectric layers comprised of the above dielectric ceramic composition only satisfies the JIS DJ or BJ characteristic and does not satisfy the X8R characteristic.
The assignee also proposed in Japanese Patent Application No. 2004-346846 a dielectric ceramic composition comprised of dielectric particles having a main ingredient phase and a diffusion phase. The dielectric ceramic composition described in this Japanese Patent Application No. 2004-346846 has a main ingredient containing barium titanate, a first sub ingredient containing at least one type of oxide selected from MgO, CaO, BaO, and SrO, a second sub ingredient including silicon oxide as its main ingredient, a third sub ingredient containing at least one type of oxide selected from V2O5, MoO3, and WO3, a fourth sub ingredient containing an oxide of R1 (where, R1 is at least one type of element selected from Sc, Er, Tm, Yb, and Lu), a fifth sub ingredient containing CaZrO3 or CaO+ZrO2, a sixth sub ingredient containing an oxide of R2 (where, R2 is at least one type of element selected from Y, Dy, Ho, Tb, Gd, and Eu), and a seventh sub ingredient containing MnO. The ratios of the sub ingredients to 100 moles of the main ingredient are as follows: first sub ingredient: 0.1 to 3 moles, second sub ingredient: 2 to 10 moles, third sub ingredient: 0.01 to 0.5 mole, fourth sub ingredient: 0.5 to 7 moles (where the number of moles of the fourth sub ingredient is the ratio of R1 alone), fifth sub ingredient: 0<fifth sub ingredient≦5 moles, sixth sub ingredient: 9 moles or less (where, the number of moles of the sixth sub ingredient is the ratio of R2 alone), and seventh sub ingredient: 0.5 mole or less.
The dielectric particles forming the dielectric ceramic composition described above have a main ingredient phase and a diffusion phase. By making the thickness of the diffusion phase, that is, the diffusion depth of the sub ingredient Ca, 10 to 30% in range of the average particle size D50 of the dielectric particles, the multilayer ceramic capacitor having dielectric layers comprised of this dielectric ceramic composition satisfies the X8R characteristic and realizes a good dielectric constant, insulation resistance (IR) life, and IR temperature dependency. However, suggestions are being sought for further improving the characteristics from other viewpoints.